In oil exploration and production fields, seawater is pumped into strategically positioned injection wells to enhance the recovery of oil from the reservoir. The recovery of oil requires injection of water into oil-bearing reservoir rock in order to move the hydrocarbons to a production well where they can be produced to the surface. The length of the pipeline from the source of the water to the oil field where it is to be injected can be thousands of kilometers. The residence time of water in the pipelines can be significant and the likelihood of the presence of conditions that promote bacteria growth is extremely high. The growth of bacteria in the pipeline can be prevented or greatly inhibited by the addition of a biocide at the water intake point that will have the effect of inhibiting bacterial growth throughout the pipeline.
The distribution pipelines normally form a grid to supply water to a number of injection wells in the vicinity of the production wells. Because of the overall length of the pipeline system, a drop in the effective concentration of biocide can occur at the point of use. The reduction in biocide concentration is due to the degradation of the active ingredient(s) present in the biocide formulation. Hence, it is important to know the actual concentration of biocide present in water at the point of use.
Biocides are also commonly added to water used in cooling towers and similar industrial systems to combat growth of bacteria. For most cooling tower installations, the degradation of the biocide is not an issue since the pipelines used with the cooling tower are not of great length; hence the concentration of biocide added remains almost constant throughout the cooling tower system. Generally, the addition of a biocide, or biocides to a distribution pipeline is at the main water intake point. For pipelines, the quantity added at the initial injection point is dependent upon the flow rate of water, ambient pipeline conditions and the length of the pipeline. The customary biocide treatment method for the biocide addition to an injection water stream is not continuous; rather, the biocide is added into the water system periodically on a fixed schedule that has been determined based on experience.
Many commonly used industrial water treatment biocide formulations contain formaldehyde and/or other compounds having an aldehyde functional group as the active ingredient to combat the growth of bacteria. After the addition of a predetermined amount of biocide over a prescribed time period (commonly referred to as a “slug”), a water sample is collected manually at various downstream sampling points and the samples are taken to a laboratory where any of a number of known analytical methods can be used to detect the presence and determine the concentration of any biocide in the sample of injection water. Once the samples have been received, the laboratory generally requires several hours to report the concentration of any biocide present in the water system. This practice is followed on a regular basis and after the addition of biocide into seawater at the point of water intake. This method of analysis is time-consuming and is not always practical at remote locations along the pipeline. Due to the complexity of some water injection networks in large oil fields, including those comprised of remote locations, the water distribution system cannot be effectively monitored by personnel at the sites for treatment and measurement of residual biocide concentration. Additionally, due to the high volumetric flow of water and pipeline length, it is often difficult to precisely determine when the biocide slug will arrive at the water sampling point, leading to a missed opportunity.
The problem addressed by the present invention is the monitoring of biocide in a stream of injection seawater on a continuous basis. Another essential aspect of the problem is to determine the concentration of biocide in the water system at the point of use, and at interim sampling points in real-time, utilizing means capable of determining the presence and also recording the concentration of the active ingredient, e.g., formaldehyde and/or other aldehyde functional groups.
Currently, there is no method or apparatus commercially available for the continuous monitoring for the presence of a biocide in an aqueous medium and no commercially available analyzer system that automatically samples, detects and measures the concentration of aldehyde-functional biocides in seawater injection distribution systems.
There is a need for in-line and real-time sensing devices for continuous monitoring of biocidal chemicals in these geographically extensive and complex water distribution systems. A system in which such test information is recorded and that is able to transmit the data from remote locations to personnel responsible for the system is needed.